The acquisition of biometric data is required for many applications. In particular, for the identification of persons and for control of authorization, the accurate and as forgery-proof as possible acquisition of this data is required. Because of their manifold advantages, touchless methods are often used thereby.
On this, a set of possibilities is described in the prior art.
According to European Patent Document EP 0 194 783 B1, a device for detection of data of uneven surfaces is known, where a transparent plate exhibits two opposing surfaces, wherein an uneven surface having recesses and protrusions, which is to be detected, is pressed against one of the even surfaces, comprising a light source for illumination of the uneven surface at the contact section through the transparent plate and an optical element for guidance of the light, which is scattered by the uneven surface, to the light detector.
The light source is arranged in such a way that it illuminates the contact section at an illumination angle which is smaller than a critical angle, in order to that the light incident from the source onto the contact section is not totally reflected, whereby a part of the light, which is scattered at the protrusions of the uneven surface, is undergoing an inner total reflection at least at the second surface of the plate, in order to propagate in a direction against the optical element, whereas the light which is scattered at the recesses is undergoing none such inner total reflection, whereby the two kinds of scattered light are separated spatially, wherein the optical element is arranged to guide only light scattered at the protrusions to the detector.
Furthermore, in European Patent Document EP 0 359 554 B1, an arrangement for the determination of fingerprints is described, with which zones of the finger are imaged to a light receiver. The arrangement possesses a light source, means for guiding the light rays which are running from the light source onto the surface of the finger to be detected, an optical imaging system which creates an image of an irradiated part of the sample, a light detector facility for detecting the image and a facility for the output of a detection signal. Using the arrangement, it shall be determined if the sample is a biological object or an imitation. Therefore, the light detector is provided with a light receiver area which is divided into zones so that an image of the irradiated part is created on the light receiver area. The light detector possesses separate optical outputs for the plurality of light rays received respectively. The discrimination if it is the matter of an authentic object, i.e. a vital finger, or an imitation is carried out by analyzing the course of the light, wherein the phenomenon that, in case of an authentic finger, the light partly enters the finger and, in case of an imitation, does not enter into it so that different courses of light result, is exploited.
In addition, according to European Patent Document EP 1 073 988 B1, a system for recognition of hand and finger lines is known, which serves for the identification of persons. Using this system, hand and/or finger lines, patterns of dermal ridges, patterns of the subcutis or the like are acquired optically for acquisition of an image by using a light source, a polarization filter and a camera without mechanical movements of the arrangement. The optical acquisition is carried out by means of polarization filters placed in the optical path of illumination and in the optical path of imaging and by means of a fixedly arranged camera.
In the case of the known arrangements, it is disadvantageous that the contrast for the imaging of the structures is low so that a secure analysis of the images is made very difficult.